The Transition Boundary Condition is used on interior boundaries to model a sheet of a medium that should be geometrically thin but does not have to be electrically thin. It represents a discontinuity in the tangential electric field. Mathematically it is described by a relation between the electric field discontinuity and the induced surface current density:

The Transition Boundary Condition section has the following material properties for the thin layer, which this boundary condition approximates:

The defaults use the values From material, taking the properties from the material specified for the boundary. For User defined enter different values or expressions.